The present invention relates to an inkjet head, and more particularly to an inkjet head provided with a piezoelectric sheet having driving electrodes formed thereon at high density.
An inkjet head provided with a piezoelectric sheet is disclosed, for example, in Japanese patent application provisional publication HEI 11-34323. FIG. 1A shows a sectional view of a part of the inkjet head disclosed in the above-mentioned publication. As shown in FIG. 1A, the inkjet head has a base plate 1010 in which a plurality of pressure chambers 1001 are formed. The inkjet head further has a conductive plate 1012, a piezoelectric layer 1003, and a plurality of driving electrodes 1002, which are laminated on the base plate 1010 in this order. The driving electrodes 1002 are formed on the piezoelectric layer 1003 at positions corresponding to respective pressure chambers 1001.
In the above-identified inkjet head, driving voltage is applied between the driving electrodes 1002 and the conductive plate 1012 so that portions of the piezoelectric layer 1003, defined therebetween, deforms due to piezoelectric effect. The deformed portions of the piezoelectric layer 1003 apply pressure to ink filled in the pressure chambers 1001 to eject the ink from nozzles (not shown) of the inkjet head.
FIG. 1B is a top view of the driving electrode 1002 of the inkjet head shown in FIG. 1A. The driving electrode 1002 has a body 1004 and an extended portion 1005. The body 1004 is formed slightly smaller than the pressure chamber 1001 and is located directly above the corresponding pressure chamber 1001. The end 1006 of the extended portion 1005 is located outside the area above the pressure chamber 1001. The end 1006 of the extended portion 1005 serves as a contact portion that is to be connected with a power supply line for applying the driving voltage to the driving electrode 1002.
Generally, a flexible printed board is connected to an inkjet head configured as above for applying driving voltage to each of the driving electrodes 1002. The flexible printed board includes a plurality of contact points arranged in a line in a vicinity of one edge thereof. The flexible printed board is electrically connected with the inkjet head by connecting those contact points with the contact portions (ends 1006) of the driving electrodes 1002. Since the contact points are arranged in a line, the driving electrodes 1002 of the inkjet head are formed and arranged such that the contact portions (ends 1006) thereof are also arranged in a line in a vicinity of one edge of the piezoelectric layer 1003.
This arrangement of the ends 1006, however, requires the extended portions 1005 of the driving electrodes 1002 to be extended from the bodies 1004 thereof for significant lengths, which in turn restricts the density of the driving electrodes 1002 formed on the piezoelectric layer 1003, the density of the pressure chambers 1001 formed right below the driving electrodes 1002, and hence the printing resolution that the inkjet head can achieve.
Therefore, there is a need for an inkjet head provided with a piezoelectric sheet having driving electrodes arranged on the piezoelectric sheet at high density.